Effects of 4-Aminopyridine on Transmission in Excitatory and Inhibitory Synapses in the Spinal Cord

Abstract

A survey of effects of 4-aminopyridine (4-AP) on synaptic transmission in the cat spinal cord (Jankowska, Lundberg, Rudomin and Syková, 1977) was made with a twofold aim: (i) to compare effects of 4-AP on excitatory and inhibitory synapses in various spinal pathways and (ii) to test these effects under conditions closest to clinical conditions, allowing comparison of effects of systemic and of local or in vitro applications. 4-AP has been found to facilitate all tested excitatory as well as inhibitory responses. It enhanced monosynaptic and polysynaptic excitation and disynaptic and polysynaptic inhibition of motoneurones, excitation of ascending tract cells and presynaptic depolarization of primary afferents; these synaptic actions were evoked by different types of afferents and various descending systems and were mediated via different interneuronal systems. In the case of the disynaptic inhibitory reflexes the evidence has been obtained that 4-AP may enhance both the excitation of the interposed interneurones and the inhibitory effects exerted by these interneurones on the motoneurones.